Experiments on Vortices in Rotating Superfluid 3He-A

A satellite peak has been observed in the NMR spectrum of rotating 3He-A; the peak intensity depends linearly on Ω at the high angular velocities, Ω=0.6−1.5 rad/s, needed to resolve it. The frequency shift of the satellite is independent of Ω. These results strongly suggest the existence of vortices in rotating 3He-A with the vortex density proportional to Ω. Another satellite peak also has been observed which probably is due to solitons.Peer reviewe

Ferromagnetic resonance in ϵ\epsilon-Co magnetic composites

We investigate the electromagnetic properties of assemblies of nanoscale $\epsilon$-cobalt crystals with size range between 5 nm to 35 nm, embedded in a polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate the samples by transmission electron microscopy (TEM) imaging, demonstrating that the particles aggregate and form chains and clusters. By using a broadband coaxial-line method, we extract the magnetic permeability in the frequency range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance with respect to an externally applied magnetic field. We find that the zero-magnetic field ferromagnetic resonant peak shifts towards higher frequencies at finite magnetic fields, and the magnitude of complex permeability is reduced. At fields larger than 2.5 kOe the resonant frequency changes linearly with the applied magnetic field, demonstrating the transition to a state in which the nanoparticles become dynamically decoupled. In this regime, the particles inside clusters can be treated as non-interacting, and the peak position can be predicted from Kittel's ferromagnetic resonance theory for non-interacting uniaxial spherical particles combined with the Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields this magnetic order breaks down and the resonant frequency in zero magnetic field reaches a saturation value reflecting the interparticle interactions as resulting from aggregation. Our results show that the electromagnetic properties of these composite materials can be tuned by external magnetic fields and by changes in the aggregation structure.Comment: 14 pages, 13 figure

Inverse Thermoreversible Mechanical Stiffening and Birefringence in a Methylcellulose/Cellulose Nanocrystal Hydrogel

We show that composite hydrogels comprising methyl cellulose (MC) and cellulose nanocrystal (CNC) colloidal rods display a reversible and enhanced rheological storage modulus and optical birefringence upon heating, i.e., inverse thermoreversibility. Dynamic rheology, quantitative polarized optical microscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and scanning and transmission electron microscopy (SEM and TEM) were used for characterization. The concentration of CNCs in aqueous media was varied up to 3.5 wt % (i.e, keeping the concentration below the critical aq concentration) while maintaining the MC aq concentration at 1.0 wt %. At 20 degrees C, MC/CNC underwent gelation upon passing the CNC concentration of 1.5 wt %. At this point, the storage modulus (G') reached a plateau, and the birefringence underwent a stepwise increase, thus suggesting a percolative phenomenon. The storage modulus (G') of the composite gels was an order of magnitude higher at 60 degrees C compared to that at 20 degrees C. ITC results suggested that, at 60 degrees C, the CNC rods were entropically driven to interact with MC chains, which according to recent studies collapse at this temperature into ring-like, colloidal-scale persistent fibrils with hollow cross-sections. Consequently, the tendency of the MC to form more persistent aggregates promotes the interactions between the CNC chiral aggregates towards enhanced storage modulus and birefringence. At room temperature, ITC shows enthalpic binding between CNCs and MC with the latter comprising aqueous, molecularly dispersed polymer chains that lead to looser and less birefringent material. TEM, SEM, and CD indicate CNC chiral fragments within a MC/CNC composite gel. Thus, MC/CNC hybrid networks offer materials with tunable rheological properties and access to liquid crystalline properties at low CNC concentrations.Peer reviewe

Разработка технологии художественного изделия из металла по технологии ковки

Выпускная квалификационная работа 80с., 24 рис., 16 табл., 10 источников, 2 прил. Ключевые слова: художественная ковка, сварка, технология, светильник, металл, бионический стиль, стилизация. Объектом исследования является технология художественной ковки, как в целом, так и применительно к конкретному изделию. Цель работы – создание декоративного напольного светильника по технологии художественной ковки. В процессе исследования проводились классификационные и комплексные анализы функций светильника, элементов конструкции, этапов формообразования и стилизации, а также свойств материалов, применяемых для создания изделия. В результате исследования были получены и классифицированы данные о различных функциях и параметрах разрабатываемого объекта, что позволило в дальнейшем создать рабочFinal qualifying work of 80c., 24 fig., 16 tab., 10 sources, 2 adj. Keywords: art forging, welding, technology, lamp, metal, bionic style, stylization. The object of research is the technology of artistic forging, both in general and in relation to a particular product. The purpose of the work - the creation of a decorative floor lamp by art forging technology. The study carried out classification and complex analyzes luminaire features design elements, the stages of shaping and styling, as well as the properties of the materials used to create the product. The study was prepared and classified data about the various features and options developed by the object, which will continue to create the workpiece in real using the claimed technology. The basic constructive, technological a

Halogenation dictates the architecture of amyloid peptide nanostructures

Amyloid peptides yield a plethora of interesting nanostructures though difficult to control. Here we report that depending on the number, position, and nature of the halogen atoms introduced into either one or both phenylalanine benzene rings of the amyloid β peptide-derived core-sequence KLVFF, four different architectures were obtained in a controlled manner. Our findings demonstrate that halogenation may develop as a general strategy to engineer amyloidal peptide self-assembly and obtain new amyloidal nanostructures

Crystalline cyclophane-protein cage frameworks

open10siCyclophanes are macrocyclic supramolecular hosts famous for their ability to bind atomic or molecular guests via noncovalent interactions within their well-defined cavities. In a similar way, porous crystalline networks, such as metal organic frameworks, can create microenvironments that enable controlled guest binding in the solid state. Both types of materials often consist of synthetic components, and they have been developed within separate research fields. Moreover, the use of biomolecules as their structural units has remained elusive. Here, we have synthesized a library of organic cyclophanes and studied their electrostatic self-assembly with biological metal-binding protein cages (ferritins) into ordered structures. We show that cationic pillar[S]arenes and ferritin cages form biohybrid cocrystals with an open protein network structure. Our cyclophane-protein cage frameworks bridge the gap between molecular frameworks and colloidal nanoparticle crystals and combine the versatility of synthetic supramolecular hosts with the highly selective recognition properties of biomolecules. Such host-guest materials are interesting for porous material applications, including water remediation and heterogeneous catalysis.openBeyeh N.K.; Nonappa; Liljestrom V.; Mikkila J.; Korpi A.; Bochicchio D.; Pavan G.M.; Ikkala O.; Ras R.H.A.; Kostiainen M.A.Beyeh, N. K.; Nonappa, ; Liljestrom, V.; Mikkila, J.; Korpi, A.; Bochicchio, D.; Pavan, G. M.; Ikkala, O.; Ras, R. H. A.; Kostiainen, M. A

Strain-Stiffening of Agarose Gels

Strain-stiffening is one of the characteristic properties of biological hydrogels and extracellular matrices, where the stiffness increases upon increased deformation. Whereas strain-stiffening is ubiquitous in protein-based materials, it has been less observed for polysaccharide and synthetic polymer gels. Here we show that agarose, that is, a common linear polysaccharide, forms helical fibrillar bundles upon cooling from aqueous solution. The hydrogels with these semiflexible fibrils show pronounced strain-stiffening. However, to reveal strain-stiffening, suppressing wall slippage turned as untrivial. Upon exploring different sample preparation techniques and rheological architectures, the cross-hatched parallel plate geometries and in situ gelation in the rheometer successfully prevented the slippage and resolved the strain-stiffening behavior. Combining with microscopy, we conclude that strain-stiffening is due to the semiflexible nature of the agarose fibrils and their geometrical connectivity, which is below the central-force isostatic critical connectivity. The biocompatibility and the observed strain-stiffening suggest the potential of agarose hydrogels in biomedical applications.Peer reviewe

Carboxymethyl Cellulose (CMC) Optical Fibers for Environment Sensing and Short-Range Optical Signal Transmission

Optical fibers are a key component in modern photonics, where conventionally used polymer materials are derived from fossil-based resources, causing heavy greenhouse emissions and raising sustainability concerns. As a potential alternative, fibers derived from cellulose-based materials offer renewability, biocompatibility, and biodegradability. In the present work, we studied the potential of carboxymethyl cellulose (CMC) to prepare optical fibers with a core-only architecture. Wet-spun CMC hydrogel filaments were cross-linked using aluminum ions to fabricate optical fibers. The transmission spectra of fibers suggest that the light transmission window for cladding-free CMC fibers was in the range of 550–1350 nm, wherein the attenuation coefficient for CMC fibers was measured to be 1.6 dB·cm–1 at 637 nm. CMC optical fibers were successfully applied in touch sensing and respiratory rate monitoring. Finally, as a proof-of-concept, we demonstrate high-speed (150 Mbit/s) short-distance signal transmission using CMC fibers (at 1310 nm) in both air and water media. Our results establish the potential of carboxymethyl cellulose-based biocompatible optical fibers for highly demanding advanced sensor applications, such as in the biomedical domain.publishedVersionPeer reviewe